Oil burner apparatus

ABSTRACT

A fuel pump unit and burner combination, an air oil mixture being recirculated vertically upwards through a central blast chamber of said burner from there outwardly and downwardly through a surrounding chamber and then again through said blast chamber for preheating prior to combustion, a refractory ring and inversion cap being positioned in the surrounding chamber and spaced above the blast chamber said unit having means for delivering only low pressure primary air and oil at atmospheric pressure to said burner.

United States Patent [72] Inventor Edgar C. Robinson North Vancouver, British Columbia, Canada [21] Appl. No. 801,445

[22] Filed Feb. 24, 1969 [45] Patented Sept. 28, 1971 [73] Assignee Dickinsons Limited Burnaby, British Columbia, Canada [32] Priority Feb. 26, 1968 [33] Canada [31 013,330

[54] 01L BURNER APPARATUS 22 Claims, 9 Drawing Figs.

[52] U.S. Cl 431/116, 431/172, 431/353, 239/318, 137/567 [51] int. Cl F231 [50] Field of Search 431/350,

[56] References Cited UNITED STATES PATENTS 3,460,895 8/1969 Yamaguchi 431/116 1,402,243 1/1922 Metcalfe 431/350 X 1,610,714 12/1926 Smith 239/318 X 2,732,890 1/1956 Vignere 431/116 3,255,804 6/1966 Lang 431/350 X 3,319,692 5/1967 Reba et a1. 431/353 X Primary Examiner-Jr. Dority Attorney-Cecil C. Kent ABSTRACT: A fuel pump unit and burner combination, an air oil mixture being recirculated vertically upwards through a central blast chamber of said burner from there outwardly and downwardly through a surrounding chamber and then again through said blast chamber for preheating prior to combustion, a refractory ring and inversion cap being positioned in the surrounding chamber and spaced above the blast chamber said unit having means for delivering only low pressure primary air and oil at atmospheric pressure to said burner.

PATENTEU SEP28 Ian sum 2 [IF 2 INVENTUR ED643 6 RUE/M504 I Li ArraR/vm hot-water-heating OIL BURNER APPARATUS BACKGROUND OF THE INVENTION This invention relates to oil-burning equipment suitable for use in a number of heating installations but particularly intended for use in domestic hot water heater.

Oil burning hot water heaters of the type used in many households are unable to operate efficiently due in part to the design of their burners and partly because the oil and air which provides the combustible mixture are both fed to the burners at quite high pressures by the conventional oil pumps and air blowers. The combustion chambers of most domestic burners are considerably smaller than that of commercial hot water heaters for example, and the high-operating pressures tend to sweep the fuel through the chambers before it can be preheated and mixed thoroughly as is necessary if a high rate of heat release is to be achieved. A high-pressure burner requires that the combustion chamber be lined with a refractory material and in order to sustain combustion this material must be incandescent. Normally, the demand for hot water is not great and, as a result, the burner operates only at fairly widely spaced intervals and then usually for only a short period of time. As a result, the burner must first be brought up to an operating temperature which will permit the fuel to burn properly and this lengthy warming up period further reduces the burners effectiveness. Because of these and other factors, conventional hot water heating equipment has been found unsatisfactory from the standpoint of economy as well as the frequent maintenance which is required to keep an inefficient burner clean and operational.

SUMMARY OF THE INVENTION fuel burned. This small and sturdy burner is fed by a unique pumping unit which supplies combustion-supporting air at a predetermined low-pressure, desirably under 10 p.s.i., and oil at atmospheric pressure. The oil is air aspirated into the burner where the air and oil are recirculated as required to ensure thorough mixing and preheating before combustion takes place. Such a burner and pumping unit combines to provide apparatus which has been found superior to the oil-burning equipment presently available for household use.

Other features and advantages of the present apparatus will be described in the following specification and be shown in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of the apparatus,

FIG. 2 is a vertical section of the burner,

FIG. 3 is a sectional plan taken on the line 3-3 of FIG. 2,

FIG. 4 is a sectional plan taken on the line 4-4 of FIG. 2,

FIG. 5 is a perspective view of the pumping unit,

FIG. 6 is a section taken on the line 6--6 of FIG. 5,

FIG. 7 is a section taken on the line 77 of FIG. 6,

FIG. 8 is an elevation of an end of the pumping unit body with parts broken away and other parts shown diagrammatically, and

FIG. 9 is a diagram showing the combined air and oil circuits.

DESCRIPTION OF THE PREFERRED EMBODIMENT The embodiment of the apparatus shown as an assembly only schematically in FIG. 1 of the drawing, comprises an oil burner 10, an ejector nozzle 11 for spraying fuel into the burner, and a pump unit 12 for supplying air and fuel to the nozzle through an air conduit 14 and an oil conduit 15. Unit 12 is adapted to be driven by an electric motor 16. A conventional electrode 17 is-provided to ignite the fuel at the start of an operating cycle of the apparatus.

Referring now particularly to FIGS. 2, 3 and 4, the oil burner generally indicated at will be seen to comprise a pot which is provided with a cylindrical wall 21 and a bottom wall 22. Wall 22 has a central opening 24. Preferably, the burner pot is fitted with legs 26 which are suitably secured as at 27 to a base plate 28 associated with a hot water heater.

Concentrically mounted within the pot 20 is'a cylindrical blast tube 30 having a lower end 31' and an upper end 32. Tube 30 is fitted with legs 34 which support said tube a short distance above the wall 22 so as to provide a small space 35 between the end 31 and the bottom wall of the burner pot. Secured to the vertically disposed tube 30, and the legs 34, is a horizontal screen 37 which is circular to fit within the cylindrical wall 21 of the pot.

Pot wall 21 has an upper edge 40 and circumferentially spaced hangers 41 are mounted on the inner surface of this wall below said upper edge. Supported on the hangers 41, a short distance below edge 41), is a refractory ring 44 having a central opening 45 and a side edge 46. This side edge of the refractory ring is spaced from the pot wall 21 to define an annular return passage 48 which leads to a recirculation chamber 50. Chamber 50 is bounded at the top by the refractory ring 44, at the bottom by the pot wall 22, and at the sides by the cylindrical walls of the burner pot and blast tube. A space 52 is formed between the underside of the ring 44 and the top edge 32 of the blast tube, this upper space being considerably larger than the lower space 35. Spaces 35 and 52 provide a preferred passage means leading from the recirculation chamber 50 to the interior of the blast tube 30. Alternatively, tube 30 may be extended so that the ends 31 and 32 thereof contact the wall 22 and ring 44. These opposite ends of the blast tube would then be slotted or perforated to provide the required passage means for placing the recirculation chamber 50 in communication with the blast tube 30.

Mounted on the burner pot 20 is an inversion cap 55 having a top wall 56 and a depending sidewall 57 which is circular and concentric to the cylindrical wall 21 of theburner pot. Cap 55 is fitted with circumferentially spaced legs 58 which are slotted as at 59 to fit over the edge 40. A combustion chamber 60 is formed between the cap 56 and the ring 44, and the space between the lower edge of wall 57 and the pot edge 40 forms a flame outlet 61 for the combustion chamber.

The pumping unit generally indicated by the numeral 12, see particularly FIGS. 5 to 8, comprises an oblong body in which a shaft 71 is rotatably mounted, the shaft being operably connected to the motor 16. Shaft 71 is journaled in bearings 72 and 73 to extend horizontally through chambers 74 and 75 (FIG. 6) formed in opposite sides of the body 70, these chambers both being eccentric to the longitudinal axis of the driven shaft. Chamber 74 houses a vane-type air pump 76 having a rotor 77 which is keyed to the driven shaft. The chamber 75 encloses an oil pump 78, this pump having a pinion 79 keyed to the end of shaft 71 and concentric thereto. The pinion meshes with an internally toothed ring gear 80 which is eccentric to the shaft 71, the ring gear being rotatably mounted in an oil pump housing 80A which is suitably secured within the chamber 75. Preferably, the chamber 75 is closed by means of a plate 81 (FIG. 6) which extends above the body 70 to form a hanger bracket 82 by which the pumping unit 12 and its driving motor 16 may be suspended from a suitable part of the hot water heater. Both the air pump 76 and the oil pump 78 are of conventional design and since their construction is quite well known and they are not considered to be novel in themselves, further detailed description of these pumping devices is considered unnecessary.

Air pump 76 is provided with an air circuit 86, shown best in FIG. 9, the conduit 14 forming part of this circuit. Circuit 86 includes a duct 87 which is formed in the air pump portion of body 70 to communicate with a circular groove 88, also formed in the aforesaid portion between the split bearing 72, see FIGS. 7 and 9.

The driven shaft 71 extends through groove 88. From the groove 83, the duct 87 extends through the body to. the intake side of the air pump. Another duct 90 connects the pressure side of the air pump to an outlet 91 and the air conduit 14 is connected to this outlet. Fitted to the body 70 is an adjusting screw 93 which extends into the duct 90. By means of the screw 93, the pressure of air delivered by the pump to the atomizing nozzle 11 can be regulated to a desired level. In the present apparatus, the air pressure may be adjusted to a selected pressure of between 3 and lbs. p.s.i.

Oil pump 78 is included in a circuit 96 (FIG. 9) which includes the oil conduit 15. As shown in FIGS. 5 and 9, a pipe 97 forms part of the circuit 96, this pipe bringing oil from a suitable source of oil supply. Pipe 97 connects with a passage 98 leading to the intake side of the oil pump. A passage 99 connects the output side of the oil pump to a pressure control valve 101 on the underside of the body 70. Valve 101 is connected by a passage 102 to a bypass valve 103 on the top of the pumping unit body and a passage 104 connects this bypass valve to the intake side of pump 78. A passage 107 extends from valve 103 to a valve 109 which is located in a reservoir 110 formed in the body 70. Reservoir 110 has an outlet 112 and the oil conduit is connected to this outlet.

Referring again to FIG. 6, valve 101 has a circular well 116 in the body 70, the well being covered by a plate 117 having a recess 118. A rubberlike diaphragm 120 is clamped between the plate 117 and the lower face of the body. Enclosed in the recess 118 is a spirally coiled spring 122 which is fitted with a disc 123, the disc bearing against the diaphragm which in turn is pressed against a raised seat 124 formed in the center of the well. An adjusting bolt 126 extends vertically through the bottom of the recessed portion of the plate 117 to bear against a cup 127 on which the spring 122 is seated. Bolt 126 is adjusted so that a force of 10 p.s.i. is required to raise the disc 123 off the seat 124. Passage 102 is formed in the body 70 to extend through the center of the seat 124, the passage being closed off by the disc 124 unless the diaphragm 120 is flexed against the pressure of the spring 122 by a predetermined pressure of oil within the well 116. Passage 99 extends into the well in spaced relation to the disc 123.

Bypass valve 103, see FIG. 6, has a well 130 covered by a plate 131 which clamps a diaphragm 132 to the body. A spring 134, mounted in a cover plate recess 135, is fitted with a disc 136, said spring exerting a force of less than 10 p.s.i. to urge the valve and diaphragm into engagement with a raised seat 137 in the center of the well. The short passage 104 provides a bypass for oil delivered to the well 130, this passage extending through the center of the seat 137 to the intake side of the oil pump. Passages 102, 105 and 107 all extend into the well 130 spaced from the disc 136.

The split bearing 72 joumaling the driven shaft 71 is lubricated by oil delivered to the air pump 76 through the passage 105, the oil moving along the driven shaft to said bearings. Bearing 73 is lubricated by oil which reaches it from the oil pump 78. A pair of lip seals 108 (FIG. 6 only) are provided in he body 70 to separate these two sources of lubricating oil. At the air pump end of the shaft, the excess oil from the air pump enters the groove 88 through which the incoming air is required to travel as it flows through the passage 87. The air flow around the groove 88 carries away excess oil, thus acting as an oil seal so that no packing glands or the like are required for the driven shaft which can then rotate with far less friction than would otherwise be the case.

Referring not to FIG. 8, the reservoir 110 will be seen to be formed in an end of the body 70, the reservoir being sealed by a gasket 140 and a closure plate 141. An air vent 142 is fitted to the top of the body 70 to extend into the reservoir and vent this chamber to atmosphere. The reservoir end of the passage 108 connects with the needle valve 109 which has an operating plunger 144. A float 145 is pivotally mounted at one end on a bar 146 which extends across the reservoir, the opposite end of the float being connected as at 147 to the plunger. Thus, when the reservoir is filled to a desired level, float 145 will pivot about the cross bar 146 and raise the plunger 144 to close the needle valve and prevent additional oil from reaching the reservoir. In his manner, oil in the reservoir is maintained at a suitable level under all normal circumstances and the reservoir can overfill only if the valve 109 or its operating parts malfunction.

In order to forestall such an occurrence, another float 150 is mounted in the upper part of the reservoir to pivot about a longitudinally extending bar 151. Above this pivot bar, the float 150 is fitted with a pin 153 which slidably extends through the body 70 and into a microswitch 154 secured to the side of said body. The microswitch has normally closed contacts 155 and 156 which are included in an electric circuit 158 connected to the electric motor 16. If for some reason, oil in the reservoir climbs above the desired level, the float will pivot to move the pin 153 endwise and open the contacts and 156. The opening of these normally closed contacts breaks the circuit 158 and cuts the power to the motor 16 so that no more oil will be pumped until the level in the reservoir drops below the upper float 150.

It will be noted the source of oil supply for the apparatus can be either an underground tank or an overhead tank. Pump 78 is capable of lifting oil from a depth of approximately 15 feet and most underground storage tanks are buried to about half this depth. In the case of an overhead tank, oil will flow by gravity to the pump 78 and may pass therethrough as far as the valve 101. Since this valve is set to open at 10 psi. there is no danger of uncontrolled flow of oil past this point.

In operation, the motor 16 drives the air pump 76 to deliver air through the circuit 86 to the nozzle 11 at a preselected pressure which may be 7 p.s.i. At the same time, the oil pump 78 forces oil through the circuit 96 to the reservoir 110 where the oil is temporarily stored at atmospheric pressure. The oil at atmospheric pressure is drawn from the reservoir through the conduit 15 and into the ejector nozzle 11 by the flow of air through the nozzle so that an atomizing mixture of air and oii is discharged into the burner 20. initially, the mixture is ignited by the electrode 17 which is energized for a period of about 1 minute until the tire within the burner pot becomes self-sustaining.

The stream of air-oil mixture is contained by the blast tube 30 and is directed through the opening 45 in the refractory ring against the inversion cap 55. During its passage through the burner, the atomized mixture is heated by the blast tube 30 and the red hot refractory ring 44. Further heat is added to the air-oil mixture by the cap 55 which also creates a back pres sure on the burner to bring about additional mixing of the combustible gases. The lighter elements of the mixture are heated sufficiently to burn and are consumed immediately in the combustion chamber 60 but some of the heavier and presumably cooler gases are deflected downwardly by the cap 55 to flow through the return annular passage 48 into the recirculation chamber 50. As these downwardly flowing gases pass the refractory ring, more heat is added and a portion of the mixture will move through the passage 52 and be reentrained in the column of air and oil being discharged from the blast tube 30. Still heavier gases flow downwardly to the bottom wall 22 and are deflected thereby through the passage 35 into the mixture stream entering the blast tube. The screen 37 increases the turbulence of the heavier gases and, in doing so, restricts any tendency the gases may have to ignite as they flow down and are heated to a temperature approaching the flash point. Finally, the heavier gases flow through the passage 35 and are carried upwardly to arrive back in the combustion chamber 60 rarefied and heated so to be readily consumed.

Thus, the mixture is prepared for combustion by being recirculated and preheated and the flame within the chamber 60 burns brightly without causing smoke or the buildup of soot. Since fuel is fed to the burner at such a low pressure, the noise which is so characteristic of conventional burners is reduced to a desirable minimum. The apparatus operates effectively regardless of the type of fuel it is required to burn and without the necessity of adjusting either the burner or the pumping unit. Tests have proven the apparatus is capable of proper operation when using any fuel from kerosene to No. 3 fuel oil. It was noted during these tests, that all these fuels were ignited quite readily even without a refractory lining for the combustion chamber and the flame within the combustion chamber was sustained without danger of blowout, this being attributed in part to the thorough mixing and preheating received by the fuels within the burner after being atomized by the nozzle.

From the foregoing, it will be apparent the apparatus is particularly well suited for use in a hot water heater or similar installation, such as the furnace of a mobile home or the like where clean and quiet operation is important, the low-pressure pumping unit and small but highly efficient burner combining to obtain maximum heat release from the fuel being burned.

It is important to note that the pump 76 supplies only primary air to the burner 10, this primary air being of sufficient quantity to draw oil from the reservoir 110 to the nozzle 11 and to discharge the oil from the nozzle into the burner. Secondary air to support combustion is induced into the burner through the bottom wall opening 24 by the kinetic energy of the oil-air mixture being injected through this opening 24. Thus, secondary air is supplied to the burner automatically and without the need of an additional air blower which is so essential to a conventional oil burner. This added advantage of the present apparatus reduces the initial cost of the hot-water-heating equipment, affords a reduction in maintenance costs and reduces the noise factor to a desirable minimum.

lclaim:

1. Oil burner apparatus comprising a burner pot having a sidewall with an upper edge and a bottom wall, air-opening means in the pot bottom, a blast tube having upper and lower ends and mounted within the burner pot, said upper end of said blast tube being disposed below said upper edge of said burner pot, a refractory ring extending across the burner pot near the upper edge thereof and spaced from the side of the pot, an inversion cap supported near the upper edge of the burner pot, said refractory ring being located between said blast tube and said inversion cap, a combustion chamber between the inversion cap and the refractory ring, passage means in the pot and in communication with the combustion chamber and with the blast tube below said refractory ring, and means for injecting a combustible mixture of air and fuel upwardly through the blast tube and the refractory ring to .impinge on the inversion cap to be burned in the combustion chamber, said inversion cap deflecting any unburned portions of the mixture downwardly through the passage means for reentrainment in the mixture flowing upwardly through the blast tube.

2. Oil burner apparatus as claimed in claim 1 in which said inversion cap is spaced above the upper edge of the burner pot to define therewith a flame outlet passage from said com bustion chamber.

3. Oil burner apparatus as claimed in claim 1 in which said passage means includes a recirculation chamber below the refractory ring, and a return passage between the combustion chamber and the recirculation chamber and defined by an outer edge surface of said refractory ring and an inner surface of said sidewall of said burner pot.

4. Oil burner apparatus as claimed in claim 1 including a flame barrier and dispersing screen extending across the burner pot intermediate the height of the blast tube.

5. Oil burner apparatus as claimed in claim 4 in which said passage means comprises an upper space between the blast tube and the refractory ring and a relatively small lower space between said blasttube and the bottom wall of the burner pot.

6. Oil burner apparatus as claimed in claim 1 in which said sidewall of the burner pot is cylindrical, said blast tube being cylindrical and concentrically mounted with respect to the sidewall of the pot.

7. Oil burner apparatus as claimedin claim 1 in which said' for directing unpressurizcd oil to the nozzle, said oil being drawn into the nozzle by the flow of air through the latter.

8. Oil burnerapparatus as claimed in claim.7 in which said oil supply means comprises a reservoir in communication with the atmosphere, pump means for supplying oilto the reservoir, float-controlled means for maintaining the oil in the reservoir at a predetermined level,,and passage means extending from the reservoir to the nozzle to direct oil to said nozzle.

9. Oil burner apparatus as claimed in claim 8 in which said air pump means and said oil pump. means comprise an air pump and a liquid pump respectively mounted for operation on a common power-driven shaft.

10. Oil burner apparatus as claimed in claim l in which said injecting means comprises a nozzle anda pumping unit, said pumping unit having a body, an air pumpjwi thin said body for supplying air at a predetermined low pressure tofthe'nozzle, an oil pump and an oil reservoir within thejbo dy, an oil circuit for transmitting pressure oil from the oil to the oil reservoir and from said oil reservoir to the nozzle, and means for maintaining the oil delivered to the nozzle at atmospheric pressure, whereby said-oil is discharged from said nozzle by the flow of air therethrough.

11. Oil burner apparatus as claimed in claim 10 including a pressure control valve in the oil circuit whereby oil below a predetermined high level is stopped from reaching the reservoir.

12. Oil burner apparatus as claimed in claim 11, and including means for controlling the level of oil in the reservoir.

13. Oil burner apparatus as claimed in claim 10 in which said air and oil pumps are driven by a common shaft, said shaft having a bearing receiving lubricating oil from the oil circuit, said body having a groove encircling the shaft at one end thereof, said air pump having an air circuit including a duct communicating with the groove whereby air flowing through said groove acts as an oil seal.

14. Oil burner apparatus as claimed in claim 4 in which said sidewall of the burner pot is of cylindrical formation, said blast tube being concentric with the cylindrical wall and having a lower end spaced above said bottom wall to provide a radially extending lower passage, and an upper end spaced from the refractory ring to provide a radially extending upper passage, said lower and upper passages forming part of said passage means.

15. Oil burner apparatus as claimed in claim 14 in which said air-opening means comprises an opening in the bottom wall of the burner pot beneath the blast tube, said injecting means being positioned to direct the combustible mixture through said opening and into the blast tube.

16. Oil burner apparatus as claimed in claim 14 including oil supply means in which said oil supply means comprises a reservoir in communication with the atmosphere, pump means for supplying oil to the reservoir, float-controlled means for maintaining the oil in the reservoir at a predetermined level, and passage means extending from the reservoir to said nozzle.

17. Oil burner apparatus as claimed in claim 16 including air pump means in which said air pump means and said oil pump means comprise an air pump and a liquid pump respectively mounted for operation on a common power-driven shaft.

18. Oil burner apparatus as claimed in claim 15 in which said injecting means comprises a pumping unit having a body, a driven shaft journaled in the body, an air pump operable by the driven shaft, a nozzle directed into the opening in he bottom wall of the burner pot, an air circuit connecting the air pump to the nozzle, an oil pump operable by the driven shaft,

'said body having a reservoir, an oil circuit for transmitting -.said air pump supplies primary air tothe burner, said primary air inducing secondary combustion-supporting air into the burner through the bottomwail opening.

20: An oil burner apparatus which comprises a burner 1 jacket having a sidewall extending from an upstream end to a downstream end of said jacket, an upstream end wall spanning said upstream end ,of said burner jacket, a blast tube having an inlet end and a discharge end and mounted within said burner jacket to define with said sidewall thereof an elongated and generally annular recirculation passage, said discharge end of said blast tube being disposed upstream of said downstream end of said burner jacket and opening generally into a primary combustion zone, a combustible mixture supply means disposed for the supply of a combustible fuel/air mixture generally axially into said inlet end of said blast tube through an opening in said upstream end wall of said burner jacket, means forming a first transfer passage for the transfer of gaseous material into said generally annular recirculation passage after the passage of such material through said blast tube, means forming a second transfer passage for the transfer of gaseous material from said annular recirculation passage into said blast tube in general proximity to said inlet end thereof, a deflector cap mounted on said burner jacket generally at said downstream end thereof to define said primary combustion zone, a centrally apertured and generally circular refractory disc mounted within said burner jacket in general proximity to said discharge end of said blast tube for impingement by gaseous material discharging therefrom, said refractory disc being of smaller diameter than said burner jacket so as to define therewith an annular gap constituting said first transfer passage and said refractory disc together with said deflector cap generally defining said primary combustion zone.

21. An oil burner apparatus as defined in claim 20 in which said inlet end of said blast tube is axially spaced apart from said upstream end wall of said burner jacket thereby to provide an annular passage constituting said second transfer passage.

22. An oil burner apparatus as defined in claim 21 in which said blast tube and said sidewall of said burner jacket are generally cylindrical, said blast tube being generally concentrically mounted so as to define with said burner jacket said recirculation passage. 

1. Oil burner apparatus comprising a burner pot having a sidewall with an upper edge and a bottom wall, air-opening means in the pot bottom, a blast tube having upper and lower ends and mounted within the burner pot, said upper end of said blast tube being disposed below said upper edge of said burNer pot, a refractory ring extending across the burner pot near the upper edge thereof and spaced from the side of the pot, an inversion cap supported near the upper edge of the burner pot, said refractory ring being located between said blast tube and said inversion cap, a combustion chamber between the inversion cap and the refractory ring, passage means in the pot and in communication with the combustion chamber and with the blast tube below said refractory ring, and means for injecting a combustible mixture of air and fuel upwardly through the blast tube and the refractory ring to impinge on the inversion cap to be burned in the combustion chamber, said inversion cap deflecting any unburned portions of the mixture downwardly through the passage means for reentrainment in the mixture flowing upwardly through the blast tube.
 2. Oil burner apparatus as claimed in claim 1 in which said inversion cap is spaced above the upper edge of the burner pot to define therewith a flame outlet passage from said combustion chamber.
 3. Oil burner apparatus as claimed in claim 1 in which said passage means includes a recirculation chamber below the refractory ring, and a return passage between the combustion chamber and the recirculation chamber and defined by an outer edge surface of said refractory ring and an inner surface of said sidewall of said burner pot.
 4. Oil burner apparatus as claimed in claim 1 including a flame barrier and dispersing screen extending across the burner pot intermediate the height of the blast tube.
 5. Oil burner apparatus as claimed in claim 4 in which said passage means comprises an upper space between the blast tube and the refractory ring and a relatively small lower space between said blast tube and the bottom wall of the burner pot.
 6. Oil burner apparatus as claimed in claim 1 in which said sidewall of the burner pot is cylindrical, said blast tube being cylindrical and concentrically mounted with respect to the sidewall of the pot.
 7. Oil burner apparatus as claimed in claim 1 in which said injecting means comprises an ejector nozzle, pump means for supplying air to and through the nozzle, and oil supply means for directing unpressurized oil to the nozzle, said oil being drawn into the nozzle by the flow of air through the latter.
 8. Oil burner apparatus as claimed in claim 7 in which said oil supply means comprises a reservoir in communication with the atmosphere, pump means for supplying oil to the reservoir, float-controlled means for maintaining the oil in the reservoir at a predetermined level, and passage means extending from the reservoir to the nozzle to direct oil to said nozzle.
 9. Oil burner apparatus as claimed in claim 8 in which said air pump means and said oil pump means comprise an air pump and a liquid pump respectively mounted for operation on a common power-driven shaft.
 10. Oil burner apparatus as claimed in claim 1 in which said injecting means comprises a nozzle and a pumping unit, said pumping unit having a body, an air pump within said body for supplying air at a predetermined low pressure to the nozzle, an oil pump and an oil reservoir within the body, an oil circuit for transmitting pressure oil from the oil pump to the oil reservoir and from said oil reservoir to the nozzle, and means for maintaining the oil delivered to the nozzle at atmospheric pressure, whereby said oil is discharged from said nozzle by the flow of air therethrough.
 11. Oil burner apparatus as claimed in claim 10 including a pressure control valve in the oil circuit whereby oil below a predetermined high level is stopped from reaching the reservoir.
 12. Oil burner apparatus as claimed in claim 11, and including means for controlling the level of oil in the reservoir.
 13. Oil burner apparatus as claimed in claim 10 in which said air and oil pumps are driven by a common shaft, said shaft having a bearing receiving lubricating oil from the oil circuit, said body having a groove encircling the shaft at one end thereof, said aIr pump having an air circuit including a duct communicating with the groove whereby air flowing through said groove acts as an oil seal.
 14. Oil burner apparatus as claimed in claim 4 in which said sidewall of the burner pot is of cylindrical formation, said blast tube being concentric with the cylindrical wall and having a lower end spaced above said bottom wall to provide a radially extending lower passage, and an upper end spaced from the refractory ring to provide a radially extending upper passage, said lower and upper passages forming part of said passage means.
 15. Oil burner apparatus as claimed in claim 14 in which said air-opening means comprises an opening in the bottom wall of the burner pot beneath the blast tube, said injecting means being positioned to direct the combustible mixture through said opening and into the blast tube.
 16. Oil burner apparatus as claimed in claim 14 including oil supply means in which said oil supply means comprises a reservoir in communication with the atmosphere, pump means for supplying oil to the reservoir, float-controlled means for maintaining the oil in the reservoir at a predetermined level, and passage means extending from the reservoir to said nozzle.
 17. Oil burner apparatus as claimed in claim 16 including air pump means in which said air pump means and said oil pump means comprise an air pump and a liquid pump respectively mounted for operation on a common power-driven shaft.
 18. Oil burner apparatus as claimed in claim 15 in which said injecting means comprises a pumping unit having a body, a driven shaft journaled in the body, an air pump operable by the driven shaft, a nozzle directed into the opening in the bottom wall of the burner pot, an air circuit connecting the air pump to the nozzle, an oil pump operable by the driven shaft, said body having a reservoir, an oil circuit for transmitting pressure oil from the oil pump to the reservoir and from said reservoir to the nozzle, and means for maintaining the oil within the oil reservoir at atmospheric pressure.
 19. Oil burner apparatus as claimed in claim 18 in which said air pump supplies primary air to the burner, said primary air inducing secondary combustion-supporting air into the burner through the bottom wall opening.
 20. An oil burner apparatus which comprises a burner jacket having a sidewall extending from an upstream end to a downstream end of said jacket, an upstream end wall spanning said upstream end of said burner jacket, a blast tube having an inlet end and a discharge end and mounted within said burner jacket to define with said sidewall thereof an elongated and generally annular recirculation passage, said discharge end of said blast tube being disposed upstream of said downstream end of said burner jacket and opening generally into a primary combustion zone, a combustible mixture supply means disposed for the supply of a combustible fuel/air mixture generally axially into said inlet end of said blast tube through an opening in said upstream end wall of said burner jacket, means forming a first transfer passage for the transfer of gaseous material into said generally annular recirculation passage after the passage of such material through said blast tube, means forming a second transfer passage for the transfer of gaseous material from said annular recirculation passage into said blast tube in general proximity to said inlet end thereof, a deflector cap mounted on said burner jacket generally at said downstream end thereof to define said primary combustion zone, a centrally apertured and generally circular refractory disc mounted within said burner jacket in general proximity to said discharge end of said blast tube for impingement by gaseous material discharging therefrom, said refractory disc being of smaller diameter than said burner jacket so as to define therewith an annular gap constituting said first transfer passage and said refractory disc together with said deflector cap generally defining said primary combustion zone.
 21. An oil burner apparatus as defined in claim 20 in which said inlet end of said blast tube is axially spaced apart from said upstream end wall of said burner jacket thereby to provide an annular passage constituting said second transfer passage.
 22. An oil burner apparatus as defined in claim 21 in which said blast tube and said sidewall of said burner jacket are generally cylindrical, said blast tube being generally concentrically mounted so as to define with said burner jacket said recirculation passage. 